In recent years, optical recording media capable of high density, high-speed recording have been keenly sought, and optical recording media capable of undergoing recording and playback with laser beam at blue wavelengths are currently being investigated as one such possibility.
In addition, amongst the optical recording media utilizing this type of blue wavelength laser light, ROM (read only memory) type optical recording media and RW (rewritable) type optical recording media have been proposed, but no write-once type optical media capable of high-speed recording with laser light of a wavelength shorter than blue wavelengths have yet been proposed.
This is because conventionally, layers with a coating of an organic dye are widely used as the recording layer of write-once type optical recording media, but these organic dyes offer inadequate recording sensitivity for high-speed recording, and if the wavelength of the laser light is shortened to improve the recording density, then synthesis of a dye suitable for use with a short wavelength laser light that is either blue or an even shorter wavelength is very difficult.
Furthermore, high-speed recording with a blue wavelength laser light that utilizes a phase-change material in the recording layer has also been proposed, but no write-once type media have been reported.
In addition, media with recording layers formed from inorganic materials also exist, but these media suffer many problems including being unsuitable for high-speed recording, offering unsatisfactory storage reliability in a recorded state, and displaying poor reproductive durability, and in all cases, the media are unsuitable for high-speed, write-once type recording.